System and method for mitigating the effects of interferers while performing conditional device scan

ABSTRACT

A method, a personal area network device operating as a slave, and a short range communications device operating as a slave are disclosed. A data storage  208  may store at least one protocol-specific channel criterion for a connection with a master short range communication device  104 . A short range transceiver  108  may execute a preliminary device scan of a scanning set of communication channels for radio frequency energy. A processor  204  may decide to execute a full device scan based in part on the protocol-specific channel criterion.

FIELD OF THE INVENTION

The present invention relates to a method and system for creating anad-hoc personal area network connection. The present invention furtherrelates to performing a conditional device scan to determine if a deviceis available for connection.

INTRODUCTION

Currently, more and more mobile telephones may use short rangecommunication technology, such as Bluetooth®, to improve functionalityand usability. Bluetooth®, and similar technology, may allow a user tocreate a personal area network, or piconet. The personal area networkmay be a network that connects multiple devices used by a single user.While the range of a personal area network may generally encompass asingle user, multiple users may use the devices of a personal areanetwork simultaneously. An example of a personal area network may be anetwork that encompasses a mobile telephone, a Bluetooth® headset, and apersonal computer or laptop. A wireless personal area network may, bynature, be ad-hoc.

In an active call using Bluetooth®, the impact that Bluetooth® has onthe total talk time for the mobile telephone may be minimal as theBluetooth® active current drain may be a small contributor to the totalmobile telephone active current drain. For example, a Bluetooth®component may use 15 mA out of over 200 mA for the entire telephone, a5% contribution. However, when a telephone is in standby with Bluetooth®on but not actively connected to a Bluetooth® headset, the effect on thephone's standby time may be significant, as much as 30%. This drain mayresult from searching for a paging signal from a paired Bluetooth®device. An inquiry scan mode current drain may also significantly impactthe phone's standby time, when the user selects the “alwaysdiscoverable” mode, which keeps the phone always in inquiry scan mode.

SUMMARY OF THE INVENTION

A method, a personal area network device operating as a slave, and ashort range communications device operating as a slave are disclosed. Adata storage may store at least one protocol-specific channel criterionfor a connection with a master short range communication device. A shortrange transceiver may execute a preliminary device scan of a scanningset of communication channels for radio frequency energy. A processormay decide to execute a full device scan based in part on theprotocol-specific channel criterion.

BRIEF DESCRIPTION OF THE DRAWINGS

Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered to be limiting of itsscope, the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 illustrates in a block diagram one embodiment of a personal areanetwork.

FIG. 2 illustrates in a block diagram one embodiment of a mobile deviceto pair with a headset.

FIGS. 3 a-d illustrate timing diagrams for establishing a Bluetooth®connection.

FIG. 4 illustrates, in a Cartesian graph, one embodiment of a firstpreliminary device scan scenario.

FIG. 5 illustrates, in a Cartesian graph, one embodiment of a secondpreliminary device scan scenario.

FIG. 6 illustrates, in a flowchart, one embodiment of a method ofexecuting an inquiry scan.

FIG. 7 illustrates, in a flowchart, one embodiment of a method ofexecuting a page scan.

FIG. 8 illustrates, in a flowchart, one embodiment of a method ofexecuting a preliminary device scan using a combinatorial criteriaanalysis.

FIG. 9 illustrates, in a flowchart, one embodiment of a method ofadjusting a scan parameter for the page scan based on power levels.

DETAILED DESCRIPTION OF THE INVENTION

Additional features and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. Thefeatures and advantages of the invention may be realized and obtained bymeans of the instruments and combinations particularly pointed out inthe appended claims. These and other features of the present inventionwill become more fully apparent from the following description andappended claims, or may be learned by the practice of the invention asset forth herein.

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

The present invention comprises a variety of embodiments, such as amethod, a mobile system, and short range communication device, and otherembodiments that relate to the basic concepts of the invention. Theshort range communication device may be any manner of computer, mobiledevice, or wireless communication device.

A method, a personal area network device operating as a slave, and ashort range communications device operating as a slave are disclosed. Adata storage may store at least one protocol-specific channel criterionfor a connection with a master short range communication device. A shortrange transceiver may execute a preliminary device scan of a scanningset of communication channels for radio frequency energy. A processormay decide to execute a full device scan based in part on theprotocol-specific channel criterion.

FIG. 1 illustrates in a block diagram one embodiment of a wirelesspersonal area network 100. A first wireless personal area networkdevice, referred to herein as a slave personal area network device 102,may execute a scan of available communication channels, referred toherein as a scanning set of communication channels, for a secondwireless personal area network device, referred to herein as the masterpersonal area network device 104, to create a connection between the twodevices. The generic scan for a master personal area network device 104is referred to herein as a device scan. The slave personal area networkdevice 102 may execute a device scan, referred to herein as an inquiryscan, for a previously unknown master personal area network device 104.The slave personal area network device 102 may then be considered pairedwith the master personal area network device 104. If the connection issevered, the slave personal area network device 102 may execute a devicescan for the now known master personal area network device 104, referredto herein as a page scan.

The power consumption of the device scan may be reduced by performing aconditional device scan to determine if a paging signal is present. In aconditional device scan, a slave personal area network device 102 mayexecute a preliminary device scan for a paging signal before executing afull device scan. The efficiency of the preliminary device scan may begreatly increased by, rather than blindly searching for the presence ofradio frequency (RF) energy, the preliminary device scan seeks RF energythat meets one or more protocol-specific channel criteria. For example,by limiting the recognition of the presence of RF energy to thosechannels of the scanning set of communication channels used by theprotocol, referred to herein as a protocol-specific channel subset, thenumber of false positives caused by environmental RF energy may begreatly reduced. If the preliminary device scan identifies a possiblesignal from the master personal area network device 102, the slavepersonal area network device 102 may then execute a full device scan forthe master personal area network device 104

A mobile system may create a short range communication connection, suchas a Bluetooth® connection, with a peripheral device, such as a headset,a memory storage device, or other mobile telephone equipment. The mobilesystem may operate as a slave short range communication device, or slavepersonal area network device 102, while a peripheral device may act as amaster short range communication device, or master personal area networkdevice 104. Alternately, the mobile system may act as a master personalarea network device 104 and the peripheral device may act as a slavepersonal area network device 102. A master Bluetooth® transceiver 106 onthe master personal area network device 104 may create a Bluetooth®connection with a slave Bluetooth® transceiver 108 on the slave personalarea network device 102.

FIG. 2 illustrates in a block diagram one embodiment of a mobile system200 or computing device 200 that may be used as a personal area networkdevice, or a short range communication device. The computing device 200may access the information or data stored in a network device. Thecomputing device 200 may support one or more applications for performingvarious communications with the network device. The computing device 200may implement any operating system, such as Windows or UNIX, forexample. Client and server software may be written in any programminglanguage, such as C, C++, Java or Visual Basic, for example. Thecomputing device 200 may be a mobile phone, a laptop, a personal digitalassistant (PDA), automotive Telematics unit, or other portable device.For some embodiments of the present invention, the computing device 200may be a WiFi or Bluetooth® capable device. The computing device 200 mayinclude a network interface 202, such as a transceiver, to send andreceive data over the network.

The computing device 200 may include a controller or processor 204 thatexecutes stored programs. The controller or processor 204 may be anyprogrammed processor known to one of skill in the art. However, thedisclosed method may also be implemented on a general-purpose or aspecial purpose computer, a programmed microprocessor ormicrocontroller, peripheral integrated circuit elements, anapplication-specific integrated circuit or other integrated circuits,hardware/electronic logic circuits, such as a discrete element circuit,a programmable logic device, such as a programmable logic array, fieldprogrammable gate-array, or the like. In general, any device or devicescapable of implementing the disclosed method as described herein can beused to implement the disclosed system functions of this invention.

The computing device 200 may also include a volatile memory 206 and anon-volatile memory 208 to be used by the processor 204. The volatile206 and nonvolatile data storage 208 may include one or more electrical,magnetic or optical memories such as a random access memory (RAM, cache,hard drive, or other memory device. The memory may have a cache to speedaccess to specific data. The memory may also be connected to a compactdisc-read only memory (CD-ROM), digital video disc-read only memory(DVD-ROM, DVD read write input, tape drive or other removable memorydevice that allows media content to be directly uploaded into thesystem.

The computing device 200 may include a user input interface 210 that maycomprise elements such as a keypad, display, touch screen, or any otherdevice that accepts input. The computing device 200 may also include auser output device that may comprise a display screen and an audiointerface 212 that may comprise elements such as a microphone, earphone,and speaker. A short range transceiver 108 may be connected to thecomputing device via a component interface 214. The short rangetransceiver 108 may conform to Bluetooth® protocol. Finally, thecomputing device 200 may include a power supply 216.

Client software and databases may be accessed by the controller orprocessor 204 from the memory, and may include, for example, databaseapplications, word processing applications, video processingapplications as well as components that embody the disclosedfunctionality of the present invention. The user access data may bestored in either a database accessible through a database interface orin the memory. The computing device 200 may implement any operatingsystem, such as Windows or UNIX, for example. Client and server softwaremay be written in any programming language, such as C, C++, Java orVisual Basic, for example.

The slave personal area network device 102 may perform a page scan toconnect to the master personal area network device 104. FIG. 3 aillustrates a timing diagram for the paging operation 300 for a masterpersonal area network device 104. In a normal page scan procedure, themaster personal area network device 104 may execute a paging procedure300. The master personal area network device 104, or paging device, maytransmit 16 frequencies in a first hop train 301 and repeat 128 timesfor a 1.28 second paging train 302, and then another 16 frequencies in asecond hop train 303 similarly repeated 128 times for the next 1.28second paging train 304 in an attempt to find the slave personal areanetwork device 102. The master personal area network device 104 may usea 32 hop pattern. The master personal area network device 104 may usethe device address, such as a Bluetooth® device address (BD_ADDR), ofthe slave personal area network device 102 to determine the page hoppingsequence. The master personal area network device 104 may split the pagehopping sequence into a first 16 hop train 301 and a second 16 hop train303 to try and connect faster. The first hop train 302 may contain hopsthat are closest to where the slave personal area network device 102 isestimated to be. The master personal area network device 104 mayestimate the phase of the clock from known information, such as the lastencounter or the inquiry procedure.

The paging operation may have a transmission slot 305 and a receptionslot 306. FIG. 3 b illustrates a close up of the slots 310 shown in FIG.3 a. During each transmission slot 305 (corresponding to the darkslots), the master Bluetooth® device may sequentially transmit a firstpaging burst 312 on a first hop frequency and a second paging burst 314on a second hop frequency. Subsequent transmission slots 305 may have afirst paging burst 312 and a second paging burst using other hopfrequencies. An intra-slot delay 316 may occur between two adjacentpaging bursts in the same transmission slot 305. An inter-slot delay 318may occur between two adjacent paging bursts in different transmissionslots 305. During each reception slot 306 (corresponding to the blankslots), the master personal area network device 104 may listen tocorresponding two hop frequencies.

As show in FIG. 3 c, the slave Bluetooth® device may perform a normaldevice scan 320. The slave personal area network device 102 may enter awakeup period 322 every 1.28 seconds and monitor a frequency to see ifthe master personal area network device 104 is attempting to connect.The slave personal area network device 102 may continue this procedureuntil the slave personal area network device 102 receives a page fromthe master personal area network device 104 and replies appropriately orthe procedure is aborted.

The slave personal area network device 102 may detect the masterpersonal area network device 104, at which point the slave personal areanetwork device 102 and the master personal area network device 104 mayenter a page response state 324. The slave personal area network device102 may enter the page response state 324 first by sending the firstresponse. Then the master personal area network device 104 may enter thepage response state 324 by sending a frequency hopping selection (FHS)packet. The slave personal area network device 102 may respond withanother identifier (ID) packet. During the next slot, both devices maystart communicating using a piconet hopping sequence derived from theBD_ADDR of the master personal area network device 104. The masterpersonal area network device 104 may send a “POLL” as the first packetand the slave personal area network device 102 may respond with any typeof packet, such as a “NULL”.

Rather than waste energy by continually performing a full page scan, theslave personal area network device 102 may execute a “conditional devicescan” 330, as shown in FIG. 3 d. A “conditional device scan” may referto the generic concept of the slave personal area network device 102waking up and performing a preliminary device scan 332 of all theavailable communication channels, referred to herein as the scanning setof communication channels, for the presence of any radio frequency (RF)energy prior to the normal page scan wakeup interval. For example, thescanning set of communications channels may be the 79 Bluetooth®channels. If no radio frequency energy is detected on any of the 79Bluetooth® channels, the slave personal area network device 102 may optto omit performing the subsequent full duration device scan 322. A fullduration device scan 322 may refer to an 11.25 millisecond scan. Theconditional device scan may significantly reduce the average device scancurrent drain of the slave personal area network device 102. If theslave personal area network device 102 detects energy in the Bluetooth®2.4 GHz industry, scientific, or medical (ISM) band during the pre-scan332, then a normal full duration device scan 322 may be performed. Thecurrent drain of the phone may be higher if both the preliminary devicescan 332 and normal full duration device scan 322 are constantly beingtriggered. This current drain may be reduced by minimizing false detectsin the preliminary device scan 332.

The slave personal area network device 102 may quickly scan the fullfrequency band over all 79 Bluetooth® channels, or the 2.4 GHz ISM band,for a duration long enough to determine if energy is present on any ofthe channels, indicating the possible presence of a personal areanetwork device. Using known information about the page and inquiry scanprocess, the conditional device scan may be enhanced for interferenceheavy environments. The slave personal area network device 102 maydetect RF energy quickly on all 79 Bluetooth® channels, recordingreceived signal strength indication (RSSI) information for the channelsfor at least 1250 microseconds, or 19 sweeps each lasting about 68microseconds. RSSI may refer to any indication of RF energy detected inthe frequency band.

The slave personal area network device 102 may systematically monitoractivity in a subset of frequencies in the ISM band trying to quicklyidentify the unique full paging or inquiry transmission signature of themaster personal area network device 104. The slave personal area networkdevice 102 may use a variety of protocol-specific channel criteriapresent in the paging signature to differentiate between a paging signalfrom the master personal area network device 104 and an interferencesource, such as a wireless local area network (WLAN) or another RFenergy source.

The master personal area network device 104 may transmit pages on 32 ofthe 79 available channels as determined by the Bluetooth® address of theslave personal area network device 102, which is the same subset of thecommunication channels the slave Bluetooth® device 104 monitors in afull page scan mode. The slave personal area network device 102 may knowthe master frequency hopping pattern, or sequence. Specifically, thechannel over which a page is sent may predetermine the channel overwhich the next page may be sent. Each page transmission may be about 1MHz in bandwidth. The duration of the transmit paging burst of themaster personal area network device 104 may be 68 microseconds induration. The time delay between subsequent paging bursts from themaster personal area network device 104 may be defined, such as 244.5microseconds, corresponding to an intra-slot delay 316, or 869.5microseconds, corresponding to an intra-slot delay 318, for an R1 pagescan.

By generating a detection signal to trigger a full device scan based ona specific type of RF activity in the ISM band rather than simply on anyform of activity, the number of times a full duration device scan isinitiated in an interference environment may be reduced, savingsignificant standby current drain while still recognizing the pagingsignature of the master personal area network device 104.

Interferers may result from a variety of sources, as may be shown by anumber of preliminary device scan scenarios. FIG. 4 illustrates, in aCartesian graph, one embodiment of a first preliminary device scanscenario 400. A wideband interferer, such as Institute of Electrical andElectronic Engineers (IEEE) standard 802.11b device, may be presentduring an initial sweep of the about 19 sweeps of the entire band withinthe 1250 microsecond preliminary device scan. Due to the presence of802.11b signal, the RSSI information on multiple frequencies may behigher than the threshold. When multiple frequencies are detected, if acertain frequency has an RSSI which is greater than the RSSI at otherdetected frequencies, the desired Bluetooth® signal may be present atthat frequency. The slave personal area network device 102 may confirmby checking for the presence of energy previous or next to the certainfrequency in the page hopping sequence at a delay of either ˜244.5 usecor ˜869.5 usec. Depending on the requirement, the slave personal areanetwork device 102 may decide to employ additional finer details ofbandwidth and time duration before generating the detection signal. Theinitial Bluetooth® burst 402 may be on channel 49 and the secondBluetooth® burst 404 may be on channel 14, 869.5 microseconds later. Thefirst burst 402 may be partially above the 22 MHz wide WLAN 406,distinguishing the first burst 402 from interference by different a RSSIvalue or amplitude, duration of time for the burst 402, or bandwidth ofthe burst 402.

FIG. 5 illustrates, in a Cartesian graph, one embodiment of a secondpreliminary device scan scenario 500. The slave personal area networkdevice 102 may detect the presence of energy on one 502 of thefrequencies present in the page hopping sequence during the initialsweeps. But, following that a wideband interferer may turn “ON” and theslave personal area network device 102 may detect multiple frequencieswith RSSI above the threshold in the latter sweeps. As in the previousscenario, the slave personal area network device 102 may look forpresence of energy in the channel which is previous or next to afrequency in the page hopping sequence at a delay of either about 244.5microseconds or 869.5 microseconds. If the slave personal area networkdevice 102 confirms the presence of energy, then the slave personal areanetwork device 102 may generate a detect signal. The initial Bluetooth®burst 502 may be on channel 49 and the second Bluetooth® burst 504 maybe on channel 14, 869.5 microseconds later. The second Bluetooth® burst504 may be partially above the 22 MHz wide WLAN 506, thus allowing theslave personal area network device 102 to distinguish the secondBluetooth® burst from interference by a different RSSI value oramplitude, duration of time for the burst, or bandwidth of the burst.

In a third scenario, during the initial sweeps, the slave personal areanetwork device 102 may detect a narrowband interferer signal of 1 MHz atchannel 49, one of the 32 page hopping frequencies of the slave. Theslave personal area network device 102 may then look for the presence ofenergy at channel 14 at a delay of about 244.5 microseconds or about869.5 microseconds. But, during the later sweeps, a wideband interferermay turn “ON”, leading the slave personal area network device 102 todetect RSSI above the threshold at channel 14. The slave personal areanetwork device 102 may compare the energy levels of neighboringfrequency channels 15 and 16. The slave Bluetooth® device may determinethat they have the same RSSI as channel 14, meaning the signal detectedon channel 49 is interference and not the desired Bluetooth® signal.Hence, the slave personal area network device 102 may omit generatingthe detection signal.

Note that in the above scenarios, the Bluetooth® signal may be presumedto be stronger than the WLAN signal if both are present at the samefrequency at the same time. Empirical data suggests that the Bluetooth®device may, in many cases, override the interference present in signalstrength given a reasonable spatial separation. However, in a few casesthe interferer may be too strong for the Bluetooth® signal, preventingeven a normal page scan from working as intended. Furthermore, the slavepersonal area network device 102 may expect the two Bluetooth® bursts tohave nearly identical RSSI values, because during the less than amillisecond lapse in time between the two bursts the RF may not degradesignificantly.

A conditional inquiry scan may be similar to a conditional page scan.The slave personal area network device 102 may determine the inquirymode hopping frequencies by using the general inquiry access code(GIAC). The 32 inquiry frequencies and order may be assumed to be thesame, with only the phase in the sequence changing, allowing the use ofthe same 32 frequencies and order for analysis instead of determiningthe frequencies and order for each device.

FIG. 6 illustrates, in a flowchart, one embodiment of a method 600 ofexecuting an inquiry scan to initially establish a pairing between themaster personal area network device 104 and the slave personal areanetwork device 102. The slave personal area network device 102 maydetermine an inquiry frequency hopping pattern to be followed on aninquiry scan based on a GIAC (Block 602). The slave personal areanetwork device 102 may execute a preliminary device scan, or preliminaryinquiry scan, for RF energy based in part on the inquiry frequencyhopping pattern (Block 604). If no inquiry RF energy level is above anenergy threshold on an inquiry channel of the inquiry frequency hoppingpattern (Block 606), the slave personal area network device 102 may waituntil the next preliminary inquiry scan is to be performed (Block 604).If an inquiry RF energy level is above an energy threshold on an inquirychannel of the inquiry frequency hopping pattern (Block 606), the slavepersonal area network device 102 may execute a full device scan, or fullinquiry scan (Block 608). If the slave personal area network device 102fails to detect a master personal area network device 104 (Block 610),the slave personal area network device 102 may wait until the nextpreliminary inquiry scan is to be performed (Block 604). If the slavepersonal area network device 102 detects a master personal area networkdevice 104 (Block 610), the slave personal area network device 102 maypair with the master personal area network device 104 (Block 612).

The slave personal area network device 102 may determine the paging modehopping frequencies by using the BD_ADDR of the slave personal areanetwork device 102. FIG. 7 illustrates, in a flowchart, one embodimentof a method 700 of executing a page scan to reestablish a Bluetooth®connection between previously paired devices. The slave personal areanetwork device 102 may store one or more channel criterion set duringchipset or product design (Block 702). The slave personal area networkdevice 102 may adjust a scan parameter of the preliminary page scanbased on scan data collected during an inquiry scan, channelclassification data, or a power condition of the slave personal areanetwork device 102 (Block 704). The scan parameter may be a set size ofthe scanning set of communication channels or the time delay betweenscanning. For example, the slave personal area network device 102 mayreduce the scanning set of communication channels, or the channelsscanned during the preliminary page scan, to those channels in thefrequency hopping pattern or in the protocol-specific channel subset.The slave personal area network device 102 may execute a preliminarydevice scan, or the preliminary page scan, for RF energy based in parton the at least one protocol-specific channel criterion (Block 706). Ifno initial RF energy level on the scanning set of communication channelsmeets the protocol-specific channel criteria (Block 708), the slavepersonal area network device 102 may wait until the next preliminarypage scan is to be performed (Block 706). If an initial RF energy levelburst meets the protocol-specific channel criteria (Block 708), theslave personal area network device 102 may decide to execute a fulldevice scan, or full page scan (Block 710). If the slave personal areanetwork device 102 fails to detect a master personal area network device104 (Block 712), the slave personal area network device 102 may waituntil the next preliminary page scan is to be performed (Block 706). Ifthe slave personal area network device 102 detects a master personalarea network device 104 (Block 712), the slave personal area networkdevice 102 may reestablish a connection with the master personal areanetwork device 104 (Block 714).

To generate the detection signal used to initiate a full page scan in amore refined manner, the slave Bluetooth® device may analyze a number ofchannel criteria to separate interference from the desired Bluetooth®signal or vice versa.

The slave personal area network device 102 may determine aprotocol-specific channel subset of a scanning set of communicationchannels for pairing with a master personal area network device 104. Outof all the scanning set of communication channels, the protocol-specificchannel subset may be those channels used by the master personal areanetwork device 102 for a paging signal as determined by the protocol.For example, the paging signal may be on one of 32 Bluetooth® channelsas determined by a device address of the slave personal area networkdevice 102, such as the slave BD_ADDR. If the detected energy is not onone of the 32 channels predetermined by the slave BD_ADDR, the detectedenergy may not be the desired page from the master personal area networkdevice 104. For a Bluetooth®—WLAN combination device the subset offrequencies to be analyzed may be reduced further depending on thechannel classification information provided by a WLAN transceiver, suchas WLAN access point frequency. The slave personal area network device102 may decide to execute a full page scan based in part on an initialRF energy level on an initial channel of the protocol-specific channelsubset during the preliminary device scan.

The slave personal area network device 102 may determine the frequencyhopping pattern for the paging. If the detected energy does not haveaccompanying energy detection on the next or previous channel in thesequence predetermined by the slave BD_ADDR within a set period, such as1250 microseconds, the detected energy may not be the desired page fromthe master personal area network device 104. The slave personal areanetwork device 102 may execute a full page scan based in part ondetecting RF energy in sequential channels of the frequency hoppingpattern.

The slave personal area network device 102 may determine the frequencybandwidth for the paging signal. If the detected energy occupies greaterthan a specific frequency bandwidth, such as 1 MHz, the detected energymay not be the desired page from the master personal area network device104. The slave personal area network device 102 may decide to execute afull page scan based in part on a frequency bandwidth of the detected RFenergy.

The slave personal area network device 102 may determine the timeduration for the paging signal. If the detected energy lasts for aduration of time longer than a specific duration, such as 68microseconds, the detected energy may not be the desired page from themaster personal area network device 104. The slave personal area networkdevice 102 may decide to execute a full page scan based in part on atime duration of the detected RF energy.

The slave personal area network device 102 may determine the time delayfor the paging signal. If two instances of detected energy are separatedby a desired amount of time, such as 244.5 microseconds or 869.5microseconds between subsequent paging bursts for an R1 page scan, thedetected energy may be the desired page from the master personal areanetwork device 104. The slave personal area network device 102 maydecide to execute a full page scan based in part on a time delay betweendetected RF energy bursts.

The slave personal area network device 102 may determine the RSSI valuesfor the detected RF energy for two or more paging channels. If thedetected energy appears in multiple energy bins with vastly differentRSSI values, the detected energy may not be the desired page from themaster personal area network device 104, since the level is anticipatedto remain relatively constant over duration between paging bursts. Theslave personal area network device 102 may decide execute a full pagescan based in part on a variance in RSSI values.

By sorting by channel and frequency hopping pattern, the slave personalarea network device 102 may minimize the occurrences of false triggersdue to interferers during a preliminary device scan. By consideringother channel criteria, the slave personal area network device 102 mayfurther improve performance. The slave personal area network device 102may scan all 79 Bluetooth® channels for 1020 microseconds, to generate adetection signal that triggers a full page scan when energy is detectedon two sequential channels from the subset of channels in the desiredBluetooth® signal paging sequence, or two positive detections insequential order of the subset of 32 out of 79 channels as dictated bythe BD_ADDR of the slave Bluetooth® device. The slave personal areanetwork device 102 may adaptively use or discard additional refinementson an as needed basis based on the signal characteristics of the desiredBluetooth® signal to distinguish the signal from the currentenvironment's interference source.

FIG. 8 illustrates, in a flowchart, one embodiment of a method 800 ofexecuting a conditional device scan using a combinatorial criteriaanalysis. The slave personal area network device 102 may determine theprotocol-specific channel subset of a scanning set of communicationchannels the master personal area network device 104 may use for pagingand the order of the protocol-specific channel subset (Block 802). Theslave personal area network device 102 may determine this information byusing the GIAC for inquiry scans or the BD_ADDR of the slave personalarea network device 102 for page scans. Nominally, the scanning set ofcommunication channels may be 1 MHz wide with at least a set size of 79,while the protocol-specific channel subset may have a subset size of 32.The slave personal area network device 102 may initiate the preliminarydevice scan of the scanning set of communication channels (Block 804).The slave personal area network device 102 may record RSSI data for the79 channels for at least 1250 microseconds (Block 806). The preliminarydevice scan may execute 19 sweeps each lasting 68 microseconds. Theslave personal area network device 102 may omit analyzing one or more ofthe following channel criteria. If the RSSI data on one of theprotocol-specific channel subset of 32 channels in the paging sequencedid not exceed a specific RSSI threshold (Block 808), the slave personalarea network device 102 may conclude that a paging sequence has not beendetected and continue with the preliminary scan (Block 810). If the RSSIdata on two sequential channels in the frequency hopping pattern did notexceed a specific RSSI threshold (Block 812), the slave personal areanetwork device 102 may conclude that a paging sequence has not beendetected and continue with the preliminary scan (Block 810). If thebandwidth of the detected energy burst exceeds a specific bandwidth,such as 1 MHz (Block 814), the slave personal area network device 102may conclude that a paging sequence has not been detected and continuewith the preliminary scan (Block 810). If the duration of the detectedenergy burst exceeds a specific duration, such as 68 microseconds (Block816), the slave personal area network device 102 may conclude that apaging sequence has not been detected and continue with the preliminaryscan (Block 810). If the delay between two detected energy bursts doesnot approximately equal a specific delay, such as 244.5 microseconds or869.5 microseconds (Block 818), the slave personal area network device102 may conclude that a paging sequence has not been detected andcontinue with the preliminary scan (Block 810). If the difference inRSSI values of two detected energy bursts exceeds a specific RSSIthreshold (Block 820), the slave personal area network device 102 mayconclude that a paging sequence has not been detected and continue withthe preliminary scan (Block 810). The slave personal area network device102 may execute a full device scan if all these criteria are met (Block822).

In another embodiment, the slave personal area network device 102 maydetermine the subset of channels to be analyzed when the device isperforming both page and inquiry scans. The slave personal area networkdevice 102 may then analyze a subset of channels. The subset of channelsmay be a combination of 32 page scan frequencies based on the BD_ADDR ofthe slave personal area network device 102 and the 32 inquiry scanfrequencies based on the GIAC. The total number of channels analyzed maybe less than 64 channels.

In another embodiment, the information obtained from the conditionaldevice scan may be further used to optimize the parameters of the fullduration page or inquiry scan. For example, depending on the frequenciesof the detected energy and the Bluetooth® address of the device, thedelay between two consecutive page scans may be modified to optimizecurrent drain. If the device is in interlaced scan mode, depending onthe frequencies of the detected energy, the device may change thefrequencies scanned in the subsequent interlaced page scan interval. Forexample, if the conditional device scan shows the presence of energy inthe second train frequencies, then the slave personal area networkdevice 102 may either omit scanning the first train frequencies or flipthe order of the frequency trains during the next interlaced page scaninterval.

The slave personal area network device 102 may have a dedicatedcontroller for the conditional device scan, based on the power source ofthe slave personal area network device 102. If the slave personal areanetwork device 102 is powered through an external power source, such asan alternating current (AC) power supply, the slave personal areanetwork device 102 may operate in a continuous scan mode, such as a R0page scan mode, to connect as soon as possible. R0 page scan mode mayconsume higher current, but external power may balance out the currentdrain. The conditional device scan may optionally be enabled if thebattery level is above a threshold to prevent false triggering frompenalizing the slave Bluetooth® device battery life when already in lowbattery mode.

The slave personal area network device 102 may support adaptivefrequency hopping (AFH) when in a connected state. The slave Bluetooth®device may have obtained channel classification information as a masteror slave device in another Bluetooth® piconet. A master personal areanetwork device 104 may determine an AFH channel map based on the channelclassification information obtained from its own measurements and fromthe host of the device and from the slave personal area network device102. A slave personal area network device 102 may obtain classificationinformation from its measurements and from the host of the device. Thechannels may be classified as good, bad or unknown in the channel map. Amaster personal area network device 104 may send a channel map to itsslave personal area network device 102. The slave personal area networkdevice 102 may reduce the set size of the scanning set of communicationchannels on the basis of the channel classification information obtainedeither from the host of the slave personal area network device 102 orfrom the latest local channel classification stored in the slavepersonal area network device 102. The slave personal area network device102 may also reduce the set size of the scanning set of communicationchannels on the basis of the AFH channel map received from the master ofanother Bluetooth® piconet. The master may be a master Bluetooth® deviceor another device.

FIG. 9 illustrates, in a flowchart, one embodiment of a method 900 ofadjusting a scan parameter of the page scan based on a power conditionof the slave personal area network device 102. The slave personal areanetwork device 102 may determine the page scan frequency hop patternbased on the BD_ADDR of the slave personal area network device 102(Block 902). If the slave personal area network device 102 is poweredthrough an AC supply (Block 904), the slave personal area network device102 may perform an R0 page scan (Block 906) and disable the conditionaldevice scan for a predefined amount of time (Block 908). If the slavepersonal area network device 102 is not powered through an AC supply(Block 904), and the battery level is insufficient for a conditionaldevice scan (Block 910), the slave personal area network device 102 maydisable the conditional device scan for a predefined amount of time(Block 908). The slave personal area network device 102 may perform aconditional device scan (Block 912). The slave personal area networkdevice 102 may reduce the set size of the scanning set of communicationchannels (Block 914). The slave personal area network device 102 mayanalyze the information of the reduced subset of frequencies toconfigure a page scan or an inquiry scan (Block 916). If the slavepersonal area network device 102 receives no new information on thepower source 216 of the slave personal area network device 102 (Block918), the slave personal area network device 102 may continue to performa conditional device scan (Block 912).

Embodiments within the scope of the present invention may also includecomputer-readable media for carrying or having computer-executableinstructions or data structures stored thereon. Such computer-readablemedia can be any available media that can be accessed by a generalpurpose or special purpose computer. By way of example, and notlimitation, such computer-readable media can comprise RAM, ROM, EEPROM,CD-ROM or other optical disk storage, magnetic disk storage or othermagnetic storage devices, or any other medium which can be used to carryor store desired program code means in the form of computer-executableinstructions or data structures. When information is transferred orprovided over a network or another communications connection (eitherhardwired, wireless, or combination thereof to a computer, the computerproperly views the connection as a computer-readable medium. Thus, anysuch connection is properly termed a computer-readable medium.Combinations of the above should also be included within the scope ofthe computer-readable media.

Embodiments may also be practiced in distributed computing environmentswhere tasks are performed by local and remote processing devices thatare linked (either by hardwired links, wireless links, or by acombination thereof through a communications network.

Computer-executable instructions include, for example, instructions anddata which cause a general purpose computer, special purpose computer,or special purpose processing device to perform a certain function orgroup of functions. Computer-executable instructions also includeprogram modules that are executed by computers in stand-alone or networkenvironments. Generally, program modules include routines, programs,objects, components, and data structures, etc. that perform particulartasks or implement particular abstract data types. Computer-executableinstructions, associated data structures, and program modules representexamples of the program code means for executing steps of the methodsdisclosed herein. The particular sequence of such executableinstructions or associated data structures represents examples ofcorresponding acts for implementing the functions described in suchsteps.

Although the above description may contain specific details, they shouldnot be construed as limiting the claims in any way. Other configurationsof the described embodiments of the invention are part of the scope ofthis invention. For example, the principles of the invention may beapplied to each individual user where each user may individually deploysuch a system. This enables each user to utilize the benefits of theinvention even if any one of the large number of possible applicationsdo not need the functionality described herein. In other words, theremay be multiple instances of the electronic devices each processing thecontent in various possible ways. It does not necessarily need to be onesystem used by all end users. Accordingly, the appended claims and theirlegal equivalents should only define the invention, rather than anyspecific examples given.

We claim:
 1. A method for creating a wireless connection for a slavepersonal area network device, comprising: determining aprotocol-specific channel subset of a scanning set of communicationchannels for a preliminary device scan, the protocol-specific channelsubset being less than a full set of available protocol-specificchannels and based upon the particular channels used as part of anearlier pairing with a master personal area network device; executingthe preliminary device scan of the scanning set of communicationchannels for radio frequency energy; and deciding to execute a fulldevice scan for re-establishing a connection with the master personalarea network device based in part on an initial radio frequency energylevel on an initial channel of the protocol-specific channel subset. 2.The method of claim 1, further comprising: storing a frequency hoppingpattern for the preliminary device scan; and deciding to execute thefull device scan based in part on detecting a radio frequency energylevel in sequential channels of the frequency hopping pattern.
 3. Themethod of claim 1, further comprising: deciding to execute the fulldevice scan based in part on at least one of a frequency bandwidth of adetected radio frequency energy, a time duration of the detected radiofrequency energy, a time delay between energy bursts, and a variance inreceived signal strength indication.
 4. The method of claim 1, furthercomprising: adjusting a scan parameter of the full device scan basedupon at least one of scan data collected during an inquiry scan, channelclassification data, and a power condition of the slave personal areanetwork device.
 5. The method of claim 4, wherein the scan parameter isat least one of a time delay between scanning or a set size of thescanning set of communication channels.
 6. The method of claim 1,wherein the full device scan is at least one of a page scan and aninquiry scan.
 7. A mobile system operating as a slave in a wirelesspersonal area network, comprising: a transceiver that executes apreliminary device scan of a scanning set of communication channels forradio frequency energy; and a processor that determines aprotocol-specific channel subset of the scanning set of communicationchannels for a connection with a master personal area network device anddecides to execute a full device scan based in part on an initial radiofrequency energy level on an initial channel of the protocol-specificchannel subset, the protocol-specific channel subset being less than afull set of available protocol-specific channels and based upon theparticular channels used as part of an earlier pairing with the masterpersonal area network device.
 8. The mobile system of claim 7, whereinthe short range transceiver conforms to Bluetooth® protocol.
 9. Themobile system of claim 7, wherein the processor decides to execute thefull device scan based in part on detecting a radio frequency energylevel on sequential channels of the frequency hopping pattern.
 10. Themobile system of claim 7, wherein the processor decides to execute thefull device scan based in part on at least one of a frequency bandwidthof a detected radio frequency energy, a time duration of the detectedradio frequency energy, a time delay between energy bursts, and avariance in received signal strength indication.
 11. The mobile systemof claim 7, wherein the full device scan is an inquiry scan.
 12. Themobile system of claim 11, wherein the processor determines theprotocol-specific channel subset using a general inquiry access code.13. The mobile system of claim 7, wherein the full device scan is a pagescan.
 14. The mobile system of claim 13, wherein the processordetermines the protocol-specific channel subset using a device addressof the slave personal area network device.
 15. A short rangecommunication device operating as a slave, comprising: a data storagethat stores at least one protocol-specific channel criterion for aconnection with a master short range communication device; a short rangetransceiver that executes a preliminary device scan of a scanning set ofcommunication channels for detecting radio frequency energy; and aprocessor that decides to execute a full device scan based in part onthe protocol-specific channel criterion, wherein the radio frequencyenergy detected matches an expected condition associated with theprotocol specific criterion, and wherein the protocol-specific channelcriterion is at least one of an initial radio frequency energy level ofan initial channel of a protocol-specific channel subset correspondingto a prior pairing, a detected radio frequency energy level onsequential channels of a frequency hopping pattern, a frequencybandwidth of the detected radio frequency energy, a time duration of thedetected radio frequency energy, a time delay between energy bursts, anda variance in received signal strength indication of proximate energybursts; wherein the processor is further adapted to determine aprotocol-specific channel subset of a scanning set of communicationchannels for a preliminary device scan, the protocol-specific channelsubset being less than a full set of available protocol-specificchannels and based upon the particular channels used as part of anearlier pairing with a master personal area network device.
 16. Theshort range communication device of claim 15, wherein the short rangetransceiver conforms to Bluetooth® protocol.
 17. The short rangecommunication device of claim 15, wherein the processor adjusts a scanparameter of the full device scan based upon at least one of datacollected during an inquiry scan, channel classification data, and apower condition of the slave personal area network device.
 18. The shortrange communication device of claim 17, wherein the scan parameter is atleast one of a time delay or a set size.
 19. The short rangecommunication device of claim 15, wherein the full device scan is atleast one of a page scan and an inquiry scan.